In ink-jet technology, image quality of high-resolution images can be a function of both the ink-jet ink used to produce an image, and the print medium upon which the image is printed. Desirable attributes of print quality include saturated colors, high gloss and gloss uniformity, and freedom of grain and coalescence, among other characteristics.
Once a high-resolution image is printed, however, another major issue arises, namely, image permanence relating to how long the quality of the image will last. As the photo industry continues to move from film to digital imaging, the issue of image permanence becomes more important.
With respect to much of the print media currently on the market, printed images commonly have undesirable attributes in the area of image permanence. One such undesirable attribute is the gradual colorant-fade observed when dye-based ink-jet inks are printed on porous media. Such fade has been shown to be caused by air, and more particularly, by small amounts of ozone in the air. It appears that, over time, ozone reacts with many dyes commonly used in ink-jet inks, thus causing them to break down and to lose or diminish their intended color properties. It should be noted that dye-fade is more of a problem with certain dyes compared to others. For example, copper phthalocyanine dyes tend to be affected to a greater extent by the presence of ozone in the air than do other dye classes.
Along with dye-fade, another significant undesirable attribute is color-shift. It has been observed that when ozone reacts with some dyes, a color hue shift occurs. This effect causes a gradual change in the perceived colors of the printed image from what was originally printed.
Both of these undesirable attributes, dye-fade and color-shift, gradually modify the perception of the printed image. Because the printed image is susceptible to these significant changes over time, many have been reluctant, especially in the graphics arts and photography industries, to embrace ink-jet printing of images intended to last for a significant period of time.
As such, it would be beneficial to develop ink-jet inks that can be printed on photo media, e.g., semi-metal oxide or metal oxide-containing porous media, while minimizing the effects of exposure to atmospheric ozone.